Mutations in the beta-amyloid precursor gene (APP) as well as mutations in genes that affect the production of beta-amyloid peptides (Abeta) have been implicated in the pathogenesis of Alzheimer's disease (AD. The identification of proteins that bind to the beta-amyloid precursor protein (betaPP) could identify genes that are affected in AD. Several groups have shown that the Fe65 protein interacts with a cytoplasmic domain of betaPP that is required for clathrin-mediated endocytosis. Deletion of this domain of betaPP has been shown to reduce the internalization of betaPP. A single amino acid substitution in the protein interaction domain of Fe65 abolishes the Fe65/betaPP interaction in vitro. APP mutations have been shown to reduce the Fe65/betaPP interaction in vivo. Thus, Fe65 could be directly involved in the internalization of betaPP or participate in signal transduction events regulating this process. In this proposal, we will complete the characterization of full length mouse Fe65 cDNAs. To determine whether Fe65 is involved in the generation of Abeta, we will generate a Fe65 knockout mouse. Since Fe65 has been shown to interact with the cytoplasmic domain of betaPP, we will cross this knockout to transgenic mice overexpressing a mutant APP and determine whether Fe65 modulates Abeta production and/or plaque formation.